Battery Basics

Introduction

As battery powered device increasing in ubiquity, system EE need to have solid understand of battery chemistry, capacity, aging, and charging and discharged curve.

Overview

Chemistry
- Lithium ion/LIPO/Lithium Polymer - Rechargeable
  - Operating voltage: ~ 3V to 4.2V
- Alkaline
  - Operating voltage: 0.9V to 1.5V
- Nickel–cadmium battery (NiCD)
  - 1.2V nominal
- Nickel-Metal Hydride (NiMH)
  - 1.2V nominal
Capacity (measured in mAh)
- Lithium ion
  - ~ 3000 mAh for a typical phone
- Alkaline
  - ~1000 mAh for AAA battery
- Nickel–cadmium battery (NiCD)
  - 1000 mAh
- Nickel-Metal Hydride (NiMH)
  - 2500 - 2700 mAh
Energy Density
- Volume Metric Density (measured in W-HR/L)
  - Lithium Ion: 210
  - Nickel–cadmium battery (NiCD): 140
  - Nickel-Metal Hydride (NiMH) : 180
Charging Rate
- Measured in C
  - 1 C means it takes an hour to finish chaging from 0% to 100%; 2C means it takes 30 mins to finish charging.
Charging Curve
- Lithum ion
  - Precharge/Trickle charging (Vbat < 2.1V) -> Constant Current -> Constant Voltage (taper off at vbat ~ 4.35V) -> Charging termination (0.02C)
    - termination is based on charging current falling below a threshold rate, typically 0.02C to 0.07C
- Nickel-Metal Hydride (NiMH)
  - Trickle charging -> Constant Current -> top-off charge -> Charging termination